Fold GetSelectionWaste() into ComputeAndSetWaste()

Both `GetSelectionWaste()` and `ComputeAndSetWaste()` now are part of
`SelectionResult`. Instead of `ComputeAndSetWaste()` being a wrapper for
`GetSelectionWaste()`, we combine them to a new function
`RecalculateWaste()`.

As I was combining the logic of the two functions, I noticed that
`GetSelectionWaste()` was making the odd assumption that the
`change_cost` being set to zero means that no change is created.
However, if we build transactions at a feerate of zero with the
`discard_feerate` also set to zero, we'd organically have a
`change_cost` of zero, even when we create change on a transaction.

This commit cleans up this duplicate meaning of `change_cost` and relies
on `GetChange()` to figure out whether there is change on basis of the
`min_viable_change` and whatever is left after deducting fees.

Since this broke a bunch of tests that relied on the double-meaning of
`change_cost` a bunch of tests had to be fixed.

1 files changed, 4 insertions, 4 deletions

diff --git a/src/bench/coin_selection.cpp b/src/bench/coin_selection.cpp
index 249b76ee85..171c61c46f 100644
--- a/src/bench/coin_selection.cpp
+++ b/src/bench/coin_selection.cpp
@@ -71,15 +71,15 @@ static void CoinSelection(benchmark::Bench& bench)
         /*change_output_size=*/ 34,
         /*change_spend_size=*/ 148,
         /*min_change_target=*/ CHANGE_LOWER,
-        /*effective_feerate=*/ CFeeRate(0),
-        /*long_term_feerate=*/ CFeeRate(0),
-        /*discard_feerate=*/ CFeeRate(0),
+        /*effective_feerate=*/ CFeeRate(20'000),
+        /*long_term_feerate=*/ CFeeRate(10'000),
+        /*discard_feerate=*/ CFeeRate(3000),
         /*tx_noinputs_size=*/ 0,
         /*avoid_partial=*/ false,
     };
     auto group = wallet::GroupOutputs(wallet, available_coins, coin_selection_params, {{filter_standard}})[filter_standard];
     bench.run([&] {
-        auto result = AttemptSelection(wallet.chain(), 1003 * COIN, group, coin_selection_params, /*allow_mixed_output_types=*/true);
+        auto result = AttemptSelection(wallet.chain(), 1002.99 * COIN, group, coin_selection_params, /*allow_mixed_output_types=*/true);
         assert(result);
         assert(result->GetSelectedValue() == 1003 * COIN);
         assert(result->GetInputSet().size() == 2);